"There's no evidence to show that the activity of man is implicated in the reproductive decline here in the Jackson Valley," said Derek Craighead, director of Beringia South, a nonprofit ecology research and educational organization.

"So, the larger question becomes: If the most common raptor is suffering a population decline in this protected landscape, what's happening to other species, and to the ecosystem as a whole?"

The problem is complex in part because even some of the most basic information about red-tailed hawks is little known.

"Despite the fact that they're one of the most common raptors in North America," said Craighead, "we don't know how long red-tailed hawks live in the wild, at what age they reproduce, whether they mate for life, or even what portion of the population pairs and nests.

"We don't even know where they go when they migrate south," he added. "We can make some guesses, but no one knows for sure."

Parasites, Pesticides and Productivity

The biologists' work is based on five decades worth of dataan unusually long span of time in wildlife ecology studies. Craighead's father and uncle began compiling data on the wildlife of Jackson Valley 50 years ago.

The present team has documented a decline in the productivity of the birdsmeasured by the number of chicks that live after they leave the nestover the last 50 years.

The scientists found that 25 percent of the adult nesting pairs never laid eggs, 25 percent of all eggs that were laid never hatched, and 20 percent of the young that hatched didn't survive. Of those chicks that did survive, 37 percent died within three weeks of leaving the nest.